With so many worthy charities asking for donations, the researchers wanted to know how people make these critical decisions.

"We gave people in the United States 5 dollars that they could allocate to Hurricane Katrina victims, Indian Ocean tsunami victims, or themselves," the authors said.

"On average, people kept 1.10 dollar for themselves and donated the rest. However, the actual amount donated to each charity depended on people''s gender and moral identity," they added.

The authors described moral identity as the extent to which being moral, fair, and just is part of someone''s self-identity.

Gender identity (which generally correlates with biological sex) is defined by how much a person focuses on communal goals, like considering the welfare of others (considered "feminine") versus ‘agentic’ goals, like assertiveness, control, and focus on the self (considered "masculine’).

During the experiments, the researchers found that participants with a feminine gender identity who placed a high importance on being moral gave equally to hurricane and tsunami victims.

Participants with a masculine gender identity who valued morality gave more to Katrina victims than tsunami victims.

"These findings suggest that donations are not simply driven by cause-worthiness. Rather they may be driven by the extent of overlap people see between themselves and the donation recipient," the authors said.

The researchers concluded that organizations and donors would benefit by understanding these donation patterns.